NCERT Exemplar for Class 9 Science Chapter 13 - Why Do We Fall ill (Book Solutions)

Multiple Choice Questions

1. Which one of the following is not a viral disease? 

(a) Dengue 

(b) AIDS 

(c) Typhoid 

(d) Influenza 

Ans: (c) Typhoid 

Explanation: Typhoid is caused due to a bacteria and hence is not a viral disease.

2. Which one of the following is not a bacterial disease? 

(a) Cholera 

(b) Tuberculosis 

(c) Anthrax 

(d) Influenza 

Ans: (d) Influenza 

Explanation: Influenza is caused by a virus and thus is not a bacterial disease. 

3. Which one of the following diseases is not transmitted by mosquitoes? 

(a) Brain fever 

(b) Malaria 

(c) Typhoid 

(d) Dengue 

Ans: (c) Typhoid 

Explanation: Typhoid is transmitted through contaminated food and water. It does not need any vector for transmission.

4. Which one of the following diseases is not caused by bacteria? 

(a) Typhoid 

(b) Anthrax

(c) Tuberculosis 

(d) Malaria 

Ans: (d) Malaria 

Explanation: Malaria is caused by plasmodium, which is a type of protozoa. 

5. Which one of the following diseases is caused by protozoans? 

(a) Malaria 

(b) Influenza 

(c) AIDS 

(d) Cholera 

Ans: (a) Malaria

Explanation: Malaria is caused by protozoa called plasmodium. Hence, option A is the correct answer. 

6. Which one of the following has a long-term effect on the health of an individual? 

(a) Common cold 

(b) Chicken pox 

(c) Chewing tobacco 

(d) Stress 

Ans: (c) Chewing tobacco 

Explanation: Effect of chewing tobacco remains for a long time and can even remain after giving up the habit. Common cold and chickenpox are acute diseases and thus do not have any long term effects. Stress can be managed by doing some healthy changes in way of living.

7. Which of the following can make you ill if you come in contact with an infected person? 

(a) High blood pressure 

(b) Genetic abnormalities 

(c) Sneezing 

(d) Blood cancer 

Ans: (c) Sneezing 

Explanation: Sneezing is one of the common symptoms of cold, and many other respiratory diseases. All these diseases are infectious and thus sneezing can spread infectious disease from one person to another. Diseases mentioned in other options are non-infectious.

8. AIDS cannot be transmitted by: 

(a) Sexual contact 

(b) Hugs 

(c) Breast feeding 

(d) Blood transfusion 

Ans: (b) Hugs

Explanation: Exchange of body fluids is essential for transmission of AIDS. Hence, AIDS cannot be transmitted through hugs. Hence, option B is the correct answer. 

9. Making antiviral drugs is more difficult than making antibacterial medicines because: 

(a) Viruses make use of host machinery 

(b) Viruses are on the borderline of living and non-living 

(c) Viruses have very few biochemical mechanisms of their own 

(d) Viruses have a protein coat 

Ans: (c) viruses have very few biochemical mechanisms of their own 

Explanation: The antibacterial medicines that are used to cure bacterial infections are effective as they stop some metabolism activities in the bacteria. Since viruses have very few biological mechanisms of their own, it is more difficult to make antiviral drugs than antibacterial medicines. 

10. Which one of the following causes kala-azar? 

(a) Ascaris 

(b) Trypanosoma 

(c) Leishmania 

(d) Bacteria 

Ans: (c) Leishmania 

Explanation: Kala-azar is caused by Leishmania, which is a protozoa. 

11. If you live in an overcrowded and poorly ventilated house, it is possible that you may suffer from which of the following diseases? 

(a) Cancer 

(b) AIDS 

(c) Air-borne diseases 

(d) Cholera 

Ans: (c) Air-borne diseases 

Explanation: Air-borne diseases are diseases that can be transmitted through air. Hence, living in an overcrowded, enclosed and poorly ventilated space increases the risk of air-borne diseases.

12. Which disease is not transmitted by mosquitoes? 

(a) Dengue 

(b) Malaria 

(c) Brain fever or encephalitis 

(d) Pneumonia 

Ans: (d) Pneumonia 

Explanation: Pneumonia is transmitted through air. Rest of the diseases mentioned in other options such as dengue and malaria are transmitted through mosquitoes. 

13. Which one of the following is not important for individual health? 

(a) Living in clean space 

(b) Good economic condition 

(c) Social equality and harmony 

(d) Living in a large and well-furnished house 

Ans: (d) Living in a large and well-furnished house 

Explanation: Living in a large and well-furnished house is not important for individual health. Living in a clean space along with good economic and social conditions are essential for individual health.

14. Choose the wrong statement: 

(a) High blood pressure is caused by excessive weight and lack of exercise 

(b) Cancers can be caused by genetic abnormalities 

(c) Peptic ulcers are caused by eating acidic food 

(d) Acne in not caused by staphylococci 

Ans: (c) Peptic ulcers are caused by eating acidic food

Explanation: Peptic ulcers are caused by a bacterium known as Helicobacter pylori. Hence, option c is the correct answer. 

15. We should not allow mosquitoes to breed in our surroundings because they: 

(a) multiply very fast and cause pollution 

(b) are vectors for many diseases 

(c) bite and cause skin diseases 

(d) are not important insects 

Ans: (b) are vectors for many diseases 

Explanation: Mosquitoes serve as the mode of transmission for various dangerous diseases such as dengue and malaria. Thus, we should not allow mosquitoes should not be allowed to breed in our surroundings. Hence, option B is the correct answer. 

16. You are aware of the Polio Eradication Programme in your city. Children are vaccinated because: 

(a) vaccination kills the polio causing microorganisms 

(b) prevents the entry of polio causing organism 

(c) it creates immunity in the body 

(d) All the above 

Ans: (c) it creates immunity in the body 

Explanation: Vaccine consists of weakened or inactive antigens that provide immunity to the body against the disease causing microbes. Hence, option c is the correct answer. 

17. Viruses, which cause hepatitis, are transmitted through: 

(a) air 

(b) water 

(c) food 

(d) personal contact 

Ans: (b) water 

Explanation: Hepatitis is an infectious disease and can be transmitted from one person to another through the means of water. It is a viral disease. Hence, option b is the correct answer.

18. Vectors can be defined as: 

(a) animals carry the infecting agents from sick person to another healthy person 

(b) micro-organisms which cause many diseases 

(c) infected person 

(d) diseased plants 

Ans: (a) animals carry the infecting agents from sick person to another healthy person 

Explanation: Vectors are the live carriers of antigens that cause diseases in the people.  

Short Answer Questions

19. Give two examples for each of the following: 

(a) Acute diseases 

Ans: (a) Viral fever, Flu 

(b) Chronic diseases 

Ans: Elephantiasis, Tuberculosis (TB) 

(c) Infectious diseases 

Ans: Smallpox, Chicken pox 

(d) Non-infectious diseases 

Ans: Diabetes, Goitre

20. Name two diseases caused by Protozoans. What are their causal organisms? 

Ans: There are many diseases caused by protozoans. Two of them are: 

(i) Kala-azar caused by Leishmania

(ii) Malaria caused by plasmodium

21. Which bacterium causes peptic ulcers? Who discovered the peptic ulcer pathogen for the first time? 

Ans: Peptic ulcers are caused by Helicobactor pylori. The peptic ulcer pathogen Helicobactor pylori was discovered by Marshall and Warren for the first time. 

22. What is an antibiotic? Give two examples. 

Ans: An antibiotic is a chemical substance that kills the bacteria by blocking the biochemical pathways which are essential for them. The two examples for antibiotics are: Penicillin and Streptomycin. 

23. Fill in the blanks: 

(a) Pneumonia is an example of _______ disease. 

Ans: Bacterial 

(b) Many skin diseases are caused by ________. 

Ans: Fungi

(c) Antibiotics commonly block biochemical pathways important for the growth of ________. 

Ans: Bacteria 

(d) Living organisms carrying the infecting agents from one person to another are called____. 

Ans: Vectors 

24. Name the target organs for the following diseases: 

(a) Hepatitis targets ________. 

Ans: Liver 

(b) Fits or unconsciousness targets ________. 

Ans: Brain 

(c) Pneumonia targets ________. 

Ans: Lungs 

(d) Fungal disease targets ________. 

Ans: Skin 

25. Who discovered ‘vaccine’ for the first time? Name two diseases which can be prevented by using vaccines. 

Ans: Edward Jenner discovered a vaccine for the first time. He discovered the vaccine for smallpox. Smallpox and Polio are the two diseases that can be prevented by using vaccines. 

26. Fill in the blanks: 

(a) ________ disease continues for many days and causes ________ on the body. 

Ans: Chronic, long term effect 

(b) ________ disease continues for a few days and causes no longer term effect on the body. 

Ans: Acute 

(c) ________ is defined as physical, mental and social well-being and comfort. 

Ans: Health 

(d) Common cold is _______ disease. 

Ans: viral 

27. Classify the following diseases as infectious or non-infectious: 

(a) AIDS 

(b) Tuberculosis 

(c) Cholera

(d) High blood pressure 

(e) Heart disease 

(f) Pneumonia 

(g) Cancer 

Ans: AIDS, tuberculosis, cholera and pneumonia are classified as infectious diseases. 

High blood pressure, heart disease, and cancer are non-infectious diseases. 

28. Name any two groups of microorganisms from which antibiotics could be extracted. 

Ans: Bacteria and fungi are the two groups of microorganisms from which antibiotics could be extracted. 

29. Name any three diseases transmitted through vectors. 

Ans: Three diseases that are transmitted through vectors are: 

a) Malaria 

b) Dengue

c) Chikungunya  

Long Answer Questions

30. Explain and give reasons: 

(a) Balanced diet is necessary for maintaining a healthy body. 

Ans: A balanced diet is a diet that consists of all the nutrients such as fats, proteins, carbohydrates, vitamins, minerals, roughage and water in proper proportion. All these food nutrients are required by the body for growth and development. Hence, a balanced diet is necessary for maintaining a healthy body.

(b) Health of an organism depends upon the surrounding environmental conditions. 

Ans: Health of a person depends upon the physical, mental and social well-being of the person. These conditions are dependent upon the individual as well as the surroundings. For example: If a person lives in an unhygienic area, there is a greater risk of infectious diseases. So, the health of an organism depends upon the surrounding environmental conditions.

(c) Our surrounding area should be free of stagnant water. 

Ans: Our surrounding area should be free of stagnant water because many water borne diseases and vectors flourish in stagnant water which cause diseases in human beings. So, to prevent the spread of such diseases, we should not let stagnant water accumulate in our surroundings. 

(d) Social harmony and good economic conditions are necessary for good health.

Ans: Humans live in societies and various locales, such as villages or towns, which influence the social and physical environment that must be kept in balance. Personal hygiene is important for an individual's health. Also, a good amount of money is required for nutritious, healthy and a balanced diet. Treatment of diseases can be afforded only when an individual has a good economic condition. Hence, social harmony and good economic conditions are necessary for good health.

31. What is a disease? How many types of diseases have you studied? Give examples.

Ans: A condition of the body or some part or organ of the body in which its functions are disturbed is called disease. 

The type of diseases are: 

a) Acute Diseases: These diseases last for only a very short period of time. They do not cause long term bad effects on our health. Example, cough, cold, fever, etc. 

b) Chronic Diseases: These diseases last for a long time, even as much as a lifetime and adversely affect the health of a person. Example, AIDS, Elephantiasis, Diabetes, etc. 

c) Infectious Diseases: Diseases which spread from an infected person to a healthy person. Example, malaria, typhoid, cholera, tuberculosis, etc. 

d) Non-infectious Diseases: Diseases which do not spread from an infected person to a healthy person. Example, arthritis, Diabetes, heart disease, hypertension, cancer etc. Non-infectious diseases can be further divided into two categories: (a) Lifestyle Diseases: Diabetes, hypertension, etc. (b) Genetic Diseases: Haemophilia, sickle-cell anaemia, etc. 

32. What do you mean by disease symptoms? Explain giving two examples?

Ans: The visual changes in human beings such as a change in the functioning of any body system for the worse, gives abnormal signs for disease known as symptoms. Symptoms vary from depending upon the disease and thus give an indication of presence of a particular disease. For example: 

a) Lesions on the skin are the symptoms of chickenpox. 

b) Cough is the symptom of lung infection. 

33. Why is the immune system essential for our health? 

Ans: Immune system is a defence system of our body which helps in controlling the action of pathogens that may harm our bodies. Immune systems possess specialised cells that can kill the microbes. The entry of microbes activates our immune system and the cells are sent to kill the infecting microbes. If these cells are successful in controlling the action of microbes, we remain unaffected. This is why, immune system is very essential for our health.

34. What precautions will you take to justify “prevention is better than cure”? 

Ans: For disease prevention, adopt the following procedures.

(1) Hygienic living conditions should be maintained.

(2) Vaccination should be taken for a variety of diseases.

(3) One should eat a balanced diet so as to get all the necessary nutrients in the right proportion. 

(4) One should take regular medical check-ups in order to be sure of being medically fit. 

(5) One should have awareness about the disease and modes of transmission of the disease.  

35. Why do some children fall ill more frequently than others living in the same locality? 

Ans: Some children fall ill more often in comparison to others living in the same locality due to their weak immune system. A child may develop a weak immune system if the body is not provided with all the nutrients in the correct proportion. A child living in a congested and unhealthy environment, not getting a balanced diet and clean water may have a weak immune system and fall ill more frequently. 

36. Why are antibiotics not effective for viral disease? 

Ans: Antibiotics usually block the pathway for biochemical mechanisms of bacterial microbes and not let them harm the body they are affecting. Viruses have a limited number of biological pathways. They replicate the mechanisms of the body they are affecting. Hence, antibiotics are not effective for viral diseases. 

37. Becoming exposed to or infected with an infectious microbe does not necessarily mean developing noticeable disease. Explain.

Ans: Our body has an immune system which helps in controlling the action of disease causing microbes. Due to the presence of the immune system, our body is normally fighting off microbes. The immune system possesses specialised cells which are capable of killing the infective microbes. The entry of microbes activates our immune system and the cells are sent to kill the infecting microbes. If these cells are successful in controlling the action of microbes, we remain unaffected. So even if we are exposed to infectious microbes, it does not necessarily mean that we suffer from diseases. 

38. Give any four factors necessary for a healthy person. 

Ans: Four factors that are necessary for a healthy person are: 

(i) The living conditions should be clean and hygienic due to which air and water borne diseases will not spread. 

(ii) Personal hygiene should be taken care of as it helps in preventing spread of infectious diseases.

(iii) Balanced diet should be taken to provide proper and complete nourishment to the body. 

(iv) Immunisation and proper vaccination should be taken against severe diseases. 

39. Why is AIDS considered to be a ‘Syndrome’ and not a disease? 

Ans: AIDS is caused by HIV virus. HIV virus comes into the body through fluid exchange by the means of sexual contact or any kind of blood transfusion. The HIV virus damages the immune system of the body and due to which the body cannot fight various minor infections such as common cold. Every small cold may become pneumonia, every minor gut infection can result in severe diarrhoea with blood loss. The effects of the diseases become severe due to damaged immune systems. Since there are no specific disease symptoms for AIDS but it results in a complex disease and symptoms, therefore it is known as a syndrome.

NCERT Exemplar Solutions for Class 9 Science Chapter 13 Why Do We Fall Ill is an important study material for Class 9 students because it has a high examination mark value.  In competitive examinations, questions from this chapter are frequently asked.  Students who wish to take biology in higher studies should study this NCERT Exemplar thoroughly so that they have a good command over the topic quickly. After completing extensive research on each topic, the NCERT Exemplar Solutions for Class 9 Science Chapter 13 are created by highly experienced professors. Students can use these solutions to acquire a broad understanding of the concepts covered in this chapter while working on the textbook questions. 

The answers to the questions in the NCERT Exemplar book are included in this NCERT Exemplar Solutions Class 9 Science book. To acquire the answers, head over to vedantu. Students can access the solutions both online and offline, depending on their needs. On Vedantu, solutions are provided in PDF format, which students can download and use to get their questions answered quickly. 

Chapter Thirteen: Why do we Fall ILL

• 13.1 Health and it’s failure

• 13.2 Disease and its causes

• 13.3 Infectious and non- infectious diseases

• 13.4 Principle of treatment and prevention

Important Topics for NCERT Exemplar Class 9 Science Solutions

Health

The state of being socially, physically, and mentally healthy so that the body can function effectively is referred to as health.

Disease

A disturbance in the function or structure of any part or organ of the body is referred to as disease. Diseases can be caused by germs or viruses, or by a lack of a nutritious diet, among other things.

Types of Diseases

There are two types of diseases:  infectious and non-infectious.

1. Acute illnesses such as the flu, the common cold, and others

2. Chronic diseases such as tuberculosis, cancer, and others

Antibiotics

Antibiotics are a type of drugs or medicines that work to prevent bacteria from body using metabolic pathways that are essential for their survival. These treatments will never function against viral infections because viruses lack their own biochemical system, yet everything is still dependent on the host.

Transmission Methods of Infectious Disease

Infectious diseases are conveyed primarily through water, food, air, and direct contact from an infected person to a healthy one.

Approaches Towards Treatment  

 There are primarily two principles of infectious diseases.  Their main objective is to:

• Reduce the severity of the signs and symptoms

• Kill the bacteria that are responsible for the illnesses.

Principles of  Prevention

Infectious infections can be prevented in one of two ways:

• Preventive measures in general

• Prevention methods in specific

Few things to keep in mind from this Chapter:

• The term "health" refers to one's physical, mental, and social well-being.

• The physical environment has an impact on an individual's health.

• The two main kinds of diseases are acute and chronic.

• Infectious and noninfectious diseases are caused by a variety of factors.

• Infectious agents are conveyed through air, water, personal touch, and other means.

• A fact to live by "Prevention is always better than cure."

• By minimising the exposure to infectious agents, public health hygiene measures prevent the spread of infectious diseases.